Growth Responses of Juvenile Red Drum Sciaenops ocellatus to Dietary Phenylalanine and Tyrosine Can Be Used to Calculate the Total Aromatic Amino Acid Requirement ,

Abstract

A current priority in aquaculture is the replacement of fish meal with alternative feedstuffs to ensure the industry's sustainability. However, most alternative protein sources are deficient in at least 1 indispensable amino acid (IAA). Therefore, there is a critical need to establish refined estimates of IAA requirements of fish. The objectives of this study were to determine the total aromatic amino acid (TAAA) requirement (Phe + Tyr) and the Tyr replacement value for Phe in juvenile red drum Sciaenops ocellatus. The TAAA requirement was obtained by feeding juvenile red drum diets that contained incremental amounts of Phe (0.54, 0.84, 1.14, 1.44, 1.74, and 2.04 g/100 g dry diet) and a fixed concentration of Tyr. Because of the TAAA requirement obtained, a second feeding trial was conducted to determine the maximum Tyr replacement value for Phe when a control diet was prepared with an 80%:20% Phe-to-Tyr ratio (Phe:Tyr; 1.60 g Phe/100 g dry diet and 0.41 g Tyr/100 g), and 5 experimental diets were prepared by decreasing the inclusion of Phe and increasing the inclusion of Tyr (Phe:Tyr of 70%:30%, 60%:40%, 50%:50%, 40%:60%, and 30%:70%). Weight gain, the feed efficiency ratio, and the protein efficiency ratio increased 354%, 133%, and 134%, respectively, relative to that of fish fed the basal diet as the Phe concentration increased to 1.44 g/100 g of dry diet; at higher concentrations of Phe, no significant differences were found between treatments. Analysis of the weight gain data with a broken-line model estimated the TAAA requirement of red drum to be 2.10 g/100 g dry diet (1.69 g Phe + 0.41 g Tyr). The maximum Tyr replacement value for Phe was estimated at 40%:60% Phe:Tyr, because only fish fed the diet with a 30%:70% Phe:Tyr ratio had a significant reduction (42%) in growth performance. The TAAA requirement for maximum growth of juvenile red drum was estimated to be 2.10 ± 0.08 g/100 g dry diet. Moreover, Tyr can account for up to 60% of the TAAA requirement of juvenile red drum.